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The Mystery of the Missing Smelt

Before we address the issue of what happened to the smelt in Lake Superior, we need to know where they came from and what they did when they invaded the Great Lakes.

Where Did They Come From?

Smelt are an Atlantic Ocean fish that spawns in freshwater. To help ensure the success of Atlantic salmon stocking efforts in the Great Lakes, Michigan fishery managers stocked smelt into the St. Marys River in 1909, 1914, 1916, and 1921. None of those attempts were successful. A 1912, stocking of smelt into Crystal Lake in Michigan led to a population that eventually entered Lake Michigan through connected waters and were first found there in 1923. They quickly spread to other Great Lakes. They were first found in Lake Huron in 1925, in Lake Erie in 1932, in Lake Ontario in 1929, and Lake Superior in 1930. They were not found in the Minnesota waters of Lake Superior until 1946.

What Did They Do?

Smelt numbers in the Great Lakes increased dramatically as sea lamprey reduced or eliminated top predators like lake trout. The commercial harvest of smelt in Lake Michigan was 86,000 pounds in 1931, but rose to 4.8 million pounds in 1941. Hints as to the fate and impact of smelt in Lake Superior occurred in lakes Michigan and Huron over the winter of 1942-43 when mass mortality caused an abrupt decline. At the time, fisheries experts suspected a disease was the cause, but they had no evidence. The spring of 1944 saw the emergence of the largest year class of whitefish ever recorded for Lakes Michigan and Huron. The cisco (formerly known as lake herring) also responded with a strong year class that delayed their decline into oblivion for about ten years. Was the decline in smelt responsible for the rebound of whitefish and cisco? It is generally agreed that the reduced smelt population played a major role in the reproductive success of those two species.

Now to Lake Superior

Here again, the smelt didn’t amount to much until the lamprey took its toll on lake trout. As the lake trout population declined, smelt numbers increased exponentially. Commercial harvest of smelt in Lake Superior went from 21,000 pounds in 1953 to over 1 million pounds in the early 1960s, and then to over 4 million pounds in 1976.

However, a curious thing occurred during this meteoric rise. Despite lake trout numbers being driven down by sea lamprey, which meant that predation on cisco was minimal, cisco almost vanished in Lake Superior as they had in the other Great Lakes. Commercial fishermen at the time thought cisco numbers would skyrocket and even planned a new marketing and processing campaign.

Unfortunately, cisco began declining rather than increasing. It was surprising because the commercial fishery had been harvesting around 4 million pounds of lake trout each year BL (before lamprey). To provide that annual harvest, much more than 4 million pounds of lake trout swam in the lake. So, if for example, there were 8 million pounds of lake trout BL, and each pound of lake trout ate 1 pound of cisco per year, then without lake trout there should be 8 million more pounds of cisco in the lake annually.

So what happened? In hindsight it is clear that smelt, probably through predation on cisco larvae, caused cisco to crash as they had elsewhere in the Great Lakes, although heavy commercial fishing pressure may have played a role as well.

So — Where Did All the Smelt Go?

Remember what happened to smelt in Lakes Michigan and Huron in 1943? They inexplicably crashed in one year. The same thing happened on Lake Superior in 1979. Smelt numbers crashed and we don’t know why. On Lakes Huron and Michigan they suspected disease, but we don’t have a clue as to what happened there or in Lake Superior. In Lakes Michigan and Huron, smelt eventually gained momentum again and produced a commercial harvest of over 9 million pounds in 1958 before they declined again. Smelt in Lake Superior have not recovered from that fateful year of 1979.

It is generally agreed that the lack of a smelt comeback is because we now have a significant number of predators back in the system. Predators are feeding heavily on smelt and even prefer smelt to the more abundant cisco as food.

Chart showing the fish harvest of cisco, lake trout, smelt and sea lamprey.

Figure 1. Commercial harvest of cisco, lake trout, and smelt in Lake Superior. Commercial harvest doesn’t perfectly represent abundance because of changing net efficiencies, market demand, and regulations, but it provides the best index of abundance available. For lamprey, an index of abundance is used rather than commercial harvest.

As long as they stick around, we will probably never see the short-lived (1960 to 1978) good old days of smelt parties in the spring. There will probably always be smelt in Lake Superior and their runs will vary in size from one year to the next, but we won’t likely see the days when you could dip net a pickup load of smelt in a night or two. The numbers of lake trout (not counting cohos, chinooks, steelheads, brown trout, eelpout) that are back in Lake Superior can eat more smelt per year than were ever commercially and sport harvested from the lake, even in the smelt heyday.

What Else Can We Blame on Smelt?

Both smelt and alewives contain thiaminase -- an enzyme that destroys thiamine (Vitamin B1) and causes deficiencies in fish. It didn’t take mink farmers long to realize that when mink were fed raw smelt, they didn’t reproduce. It took longer to realize that what was described as early mortality syndrome (EMS) in lake trout and other salmonids was caused by a thiamine deficiency resulting from eating smelt and alewives. It eventually became clear that fish that fed heavily on smelt and alewives produced larvae that didn’t survive very well. This is likely slowing lake trout rehabilitation efforts in the other Great Lakes.

We have also seen impacts in inland lakes where smelt have been introduced. As smelt numbers grow, cisco numbers fall and in many cases disappear completely because the smelt eat cisco fry and fingerlings. Walleye seem to thrive on a diet of smelt and grow faster, but they aren’t able to reproduce effectively, likely because walleye fry are competing with or being preyed upon by smelt. Researchers and fishery managers have expressed concerns that walleye fry may experience EMS, as seen in many salmonids, but evidence is lacking. Yellow perch numbers in inland lakes also decline when smelt invade -- primarily through competition for food.

Summary:

The major short-term smelt crashes that we have seen in the Great Lakes remain mysterious, but the reason we can’t catch smelt like we did in the good old days is because a healthy population of lake trout (thanks to lamprey control and good fisheries management) has caught them first.

Related Content:

About smelt populations in Lake Superior:

By Jeff Gunderson
2008


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